Multidrug resistance (MDR) is the dominant challenge in the failure of chemotherapy in cancers. Phosphatidylinositol 3-kinase (PI3K) is a lipid kinase that spreads intracellular signal cascades and regulates a variety of cellular processes. PI3Ks are considered significant causes of chemoresistance in cancer therapy. Protein kinase B (AKT) is also a significant downstream effecter of PI3K signaling, and it modulates several pathways, including inhibition of apoptosis, stimulation of cell growth, and modulation of cellular metabolism. This review highlights the aberrant activation of PI3K/AKT as a key link that modulates MDR. We summarize the regulation of numerous major targets correlated with the PI3K/AKT pathway, which is further related to MDR, including the expression of apoptosis-related protein, ABC transport and glycogen synthase kinase-3 beta (GSK-3β), synergism with nuclear factor kappa beta (NF-κB) and mammalian target of rapamycin (mTOR), and the regulation of glycolysis.

Our understanding of cancer has largely come from the analysis of aberrations within the tumor cell population. Yet it is increasingly clear that the tumor microenvironment can significantly influence tumorigenesis. For example, the mesenchyme can support the growth of tumorigenic epithelium. However, whether fibroblasts are subject to genetic/epigenetic changes as a result of selective pressures conferred by oncogenic stress in the epithelium has not been experimentally assessed. Recent analyses of some human carcinomas have shown tumor-suppressor gene mutations within the stroma, suggesting that the interplay among multiple cell types can select for aberrations nonautonomously during tumor progression. We demonstrate that this indeed occurs in a mouse model of prostate cancer where epithelial cell cycle disruption via cell-specific inhibition of pRb function induces a paracrine p53 response that suppresses fibroblast proliferation in associated stroma. This interaction imposes strong selective pressure yielding a highly proliferative mesenchyme that has undergone p53 loss.

We examined the expression of calcium transporter 1 (CaT1) and epithelial calcium channel (ECaC) mRNA in the duodenum and kidney of mice. Intestinal CaT1 mRNA level increased 30-fold at weaning, coincident with the induction of calbindin-D(9k) expression. In contrast, renal CaT1 and ECaC mRNA expression was equal until weaning when ECaC mRNA is induced and CaT1 mRNA levels fall 70%. Long- and short-term adaptation to changes in dietary calcium (Ca) level and 1,25 dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] injection strongly regulated duodenal calbindin D(9k) and CaT1 mRNA. Following a single dose of 1,25(OH)(2)D(3), induction of CaT1 mRNA occurred rapidly (within 3 h, peak at 6 h of 9.6 +/- 0.8-fold) and preceded the induction of intestinal Ca absorption (significantly increased at 6 h, peak at 9 h). Neither renal CaT1 nor ECaC mRNA were strongly regulated by dietary calcium level or 1,25(OH)(2)D(3) injection. Our data indicate that CaT1 and ECaC mRNA levels are differentially regulated by 1,25(OH)(2)D(3) in kidney and intestine and that there may be a specialized role for CaT1 in kidney in fetal and neonatal development. The rapid induction of intestinal CaT1 mRNA expression by 1,25(OH)(2)D(3), and the marked induction at weaning, suggest that CaT1 is critical for 1,25(OH)(2)D(3)-mediated intestinal Ca absorption.

To study the role of calbindin D(9k) (CaBP) and epithelial calcium channel ECaC2 in intestinal calcium (Ca) absorption, vitamin D receptor knockout (KO) and wild-type (WT) mice were fed either 0.5% Ca or a 2.0% Ca rescue diet starting at 21 d of age. Ca absorption and parameters involved in this process were measured at 60 or 90 d of age. Compared with WT, KO mice fed the 0.5% Ca diet had higher plasma parathyroid hormone (PTH) and 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)], and lower plasma Ca and insulin-like growth factor-I (IGF-I). Duodenal Ca absorption (% Ca absorbed) in KO mice was reduced 71% relative to WT mice and was associated with 55% lower CaBP mRNA, 47% lower CaBP protein and 95% lower ECaC2 mRNA levels. Compared with WT mice, the percentage of Ca absorbed in KO mice fed the 0.5% Ca diet was inappropriately low for the level of duodenal CaBP. The 2% Ca rescue diet normalized plasma Ca, prevented osteomalacia, increased growth and plasma IGF-I levels, but did not normalize plasma PTH or 1,25(OH)(2)D(3) in KO mice. In addition, the relationship between CaBP protein and the percentage of Ca absorbed was normalized, whereas ECaC2 mRNA fell to near zero. Our data demonstrate that higher CaBP levels do not ensure high rates of duodenal Ca absorption and that transcellular Ca absorption can occur even when ECaC2 gene expression is very low. In addition, our data suggest that the 2% Ca diet promotes a vitamin D receptor-independent anabolic effect on bone formation and calcium absorption, leading to improved calcium balance even in the presence of high PTH levels.

The majority of human high grade serous epithelial ovarian cancer (SEOC) is characterized by frequent mutations in p53 and alterations in the RB and FOXM1 pathways. A subset of human SEOC harbors a combination of germline and somatic mutations as well as epigenetic dysfunction for BRCA1/2. Using Cre-conditional alleles and intrabursal induction by Cre-expressing adenovirus in genetically engineered mice, we analyzed the roles of pathway perturbations in epithelial ovarian cancer initiation and progression. Inactivation of RB-mediated tumor suppression induced surface epithelial proliferation with progression to stage I carcinoma. Additional biallelic inactivation and/or missense p53 mutation in the presence or absence of Brca1/2 caused progression to stage IV disease. As in human SEOC, mice developed peritoneal carcinomatosis, ascites, and distant metastases. Unbiased gene expression and metabolomic profiling confirmed that Rb, p53, and Brca1/2-triple mutant tumors aligned with human SEOC, and not with other intraperitoneal cancers. Together, our findings provide a novel resource for evaluating disease etiology and biomarkers, therapeutic evaluation, and improved imaging strategies in epithelial ovarian cancer.